1. Technical Field
The present invention relates to a power-generating apparatus that extracts electric charge generated when a piezoelectric material such as a piezoelectric device is deformed by external forces as an electric energy.
2. Related Art
When a piezoelectric material such as lead zirconate titanate (PZT), crystal (SiO2), or zinc oxide (ZnO) is deformed by external forces, electric polarization is induced within the material and positive and negative electric charge appears on the surface. This phenomenon is the so-called piezoelectric effect. A power-generating method of vibrating a cantilever and repeatedly weighting the piezoelectric material and extracting the electric charge generated on the surface of the piezoelectric material as electricity using the property of the piezoelectric material has been proposed. For example, a technology of vibrating a metal cantilever formed by providing a weight on its end and bonding a thin plate of a piezoelectric material thereto, extracting positive and negative electric charge alternately generated in the piezoelectric material with the vibration and generating an alternating current, further, rectifying the alternating current by a diode, and then, accumulating it in a capacitor and extracting it as power has been proposed (Patent Document 1 (JP-A-7-107752)).
In a power-generating apparatus using the technology, when a force beyond the scope of the assumption acts on the cantilever and the cantilever excessively vibrates, the cantilever may collide with a surrounding member and break. In order to prevent that, a technology of relaxing the impact when the cantilever collides with the inner wall of a casing containing the cantilever by providing an elastic body on the inner wall of the casing has been proposed (Patent Document 2 (JP-A-2003-218418)).
However, there has been a problem that it is difficult to sufficiently downsize the power-generating apparatus because it is necessary to secure a space for providing the elastic body in the proposed technologies in related art.